Small Engine Troubleshooting Problems? Ask a Mechanic Now.
good afternoon my name is ***** ***** I will do what I can to help you. By the sounds of it you have covered the basics by replacing the relay and switch. 2 things that come to my mind are seat switch and electric clutch
if your seat switch looses contact it will shut down the mower (and engine in most cases)
but most likely your electric clutch is at fault. take a look and see if you see any bare wires going to it. make sure the bearings aren't getting excessively worn. possibly run the machine and after it cuts out shut off the engine and take a look at the clutch. it will be warm normally but check to see if it seems excessively hot. it may have failed internally and is drawing to many amps when engaged.